The present invention relates to a vehicular air conditioning system for air conditioning the passenger compartment of the vehicle.
Generally, a vehicular air conditioning system includes a controller such as a computer. The controller controls the discharge displacement of a compressor based on external information such as the temperature in the passenger compartment, a set target temperature, and so on.
The compressor is generally driven by an internal combustion engine of the vehicle. The air conditioning system must be controlled in accordance with the driving conditions of the internal combustion engine. For this reason, the controller for the engine may sometimes serve as the aforementioned controller for the air conditioner. However, when the controller for the internal combustion engine and the controller for the air conditioning are combined, the controller is burdened with the extra duty of handling the information for controlling the air conditioning system. As a result, the controller experiences difficulties in the control of the internal combustion engine. For avoiding this problem, a separate controller is provided exclusively for controlling an air conditioning system. The controller for controlling the internal combustion engine is connected to the controller for controlling the air conditioning system through a communication line.
The compressor is one of the auxiliary machines that consumes the most power, and is a large load for the internal combustion engine. For this reason, when the power of the internal combustion engine must be maximally allocated for running the vehicle, such as when the vehicle is accelerated, the discharge displacement is minimized for reducing the load on the internal combustion engine. Such control is hereinafter referred to as the xe2x80x9cdisplacement limit controlxe2x80x9d.
When the controller for the internal combustion engine communicates with the controller for the air conditioning to minimize the discharge displacement after determining that the displacement limit control is required, a delay occurs due to the communication speed between the controllers. During this delay, the load on the internal combustion engine by driving the compressor is not reduced. In other words, the vehicle experiences degraded acceleration performance.
Recently, it has been proposed to build an on-board network that includes a controller for the internal combustion engine, a controller for the air conditioning system and other controllers (for example, a controller such as a computer for controlling the transmission). In the on-board network, communications between the controller for the internal combustion engine and the controller for the air conditioning system are performed using a common communication line, which is shared with the other controllers. When a large amount of communication between controllers causes congestion on the communication line, a larger delay occurs from the time the controller for the internal combustion engine determines that the displacement limit control is required until the time the controller for the air conditioning system minimizes the discharge displacement of the compressor.
It is an object of the present invention to provide a vehicular air conditioning system that is capable of rapidly changing the discharge displacement in accordance with the driving condition of an internal combustion engine.
In order to attain the above objective, the present invention provides a vehicle air conditioning apparatus including a refrigerant circuit. The air conditioning apparatus is driven by a power source of a vehicle. The air conditioning apparatus comprises a variable displacement compressor. An external information detector detects external information used for the air conditioning of the vehicle. A first controller controls the output of the power source. A second controller is connected to the first controller via a communication line. The second controller computes a target value of the displacement of the compressor based on the external information. The second controller sends the computed target value to the first controller. The first controller controls the displacement of the compressor based on the computed target value.
The present invention also provides a method for controlling a vehicle air conditioning apparatus including a refrigerant circuit. The air conditioning apparatus is driven by a power source of a vehicle. The method includes controlling the output of the power source by a first controller, computing a target value of the displacement of a variable displacement compressor based on an external information used for the air conditioning of the vehicle by a second controller connected to the first controller via a communication line, sending the computed target value from the second controller to the first controller, and controlling the displacement of the compressor based on the computed target value by the first controller.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.